You can use the piano roll view or the staff view of your DAW and maybe BiaB, don’t know, and write your string parts. You can use whatever strings sounds you have now. This is a slow process but it works.

You can also have BiaB generate string parts and you can modify them in the PVR or staff view. I do this a lot using my DAW.

Over on this side of the pond you can buy a new or used keyboard with a MIDI out for $100 USD or less. These will not be velocity sensitive and/or may have small keys but they will work.

Whenever I get something stuck in the back of my throat, I dislodge it by drinking a beer.
It's called the Heineken Maneuver.

64 bit Win 10 Pro, the latest BiaB/RB, Roland Octa-Capture audio interface, a ton of software/hardware